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1970 390 piston choices

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401MATCOUPE View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 401MATCOUPE Quote  Post ReplyReply Direct Link To This Post Topic: 1970 390 piston choices
    Posted: Mar/19/2012 at 4:07pm
The Chief Piston Designer at Keith Black is a fellow Studebaker Enthusiast, he has 40 plus years of internal combustion engine experience and Custom Build Pistons for the Studebaker folks all in Hyperutectic Design.  He has told me that the biggest failure issue is wrong ring gap for application.  The old .004" of end gap per inch of bore size does work on all applications. Alot of Studebakers are factory supercharged and high output (10 psi plus), using these pistons but with a larger end gap.  If you go to the Keith Black Catalog there is a great deal of info there that can be used on our AMC Performance Engines.  If you want to build a performance engine using a supercharger, turbo or nitrous, KB can give some great advise.....give John Erb a call, he is an unbelievable mountain of information.  He has been involved in 304 CID Studebakers at the Salt Flats going 200+ MPH and holding the record.  Sorry for the Brand X Orphan Car references, but if they can make that kind of power so can a "Modern AMC V-8's".
Ross K. Peterson
68X,GoPac,343,AT,52A(1stCar)
68X,GoPac,390,4sp,52A
69X,GoPac,390,4sp,64A
70X,GoPac,390,4sp,87A,8
70X,GoPac,390,4sp,BBO,8
70 Jav SST,390,AT,BSO
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smills61074 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/17/2012 at 8:52pm
It appears everyone seems to recommend forged.  I guess I will have to wait until I get my block checked out at the machine shop,  Then I will know what size I will need.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 440sixpack Quote  Post ReplyReply Direct Link To This Post Posted: Mar/11/2012 at 9:06am
Dan is correct don't have it in the hole that's a sure prescription for trouble, Bulltear will take your specs and make sure you are flat . 
 
 You didn't say if you have a standard bore or not, if you're headed to a .60 over  like I have to go you better have your shop sonic the block before you go any deeper.  I guess AMC can have a little core shift too.
 
 
There are lots of good pistons out there but when you can just make a phone call and get a set of american made customs to fit your needs  for $600 it's a no brainer for me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/10/2012 at 10:05pm
Custom pistons are just that, custom. You can have them made to fit your specfic engine's deck, bore and valve relief to have whatever compression you want.
Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 74Bubblefender Quote  Post ReplyReply Direct Link To This Post Posted: Mar/10/2012 at 10:00pm
China...heck no. Zero deck is what you want with a nice shaped D-dish
We are just about to forge new AMC V8 crankshafts.. please check here
http://www.bulltear.com/forums/showthread.php?19564
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smills61074 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/10/2012 at 9:21pm
Are the bulltears made in chna?  If I go with a 401 crank, will my pistons still be down in the hole?  I am taking my block to the machine shop this week.  Once it is boiled and magnifluxed, I will know if I have to go oversize with the pistons.  Everyone, thanks for your help.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 440sixpack Quote  Post ReplyReply Direct Link To This Post Posted: Mar/09/2012 at 10:26pm

 If your detonation is bad enough to take out a piston you  need to do something about it .  no piston will take it forever,  granted forged will last the longest.

 This pretty much covers it.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 17tamx Quote  Post ReplyReply Direct Link To This Post Posted: Mar/09/2012 at 9:16pm
401 pistons in a 70 390 block will be .060" down the hole and you will have pinging problems if not addressed.
 
I decked my 70 390 block .060" to get to zero deck height. I am using the Speed-pro forged 401 pistons with the .170" dish.
 
I took .024" off of my 291C heads to get me to 10.71:1 and I run standard 91 octane pump gas here in Phoenix without any detonation.
 
It took 312 grams of mallory metal to switch from external to internal balance. If I had used the lighter  more expensive forged pistons the pistons would not have been $333.00 from summit but I would have saved money on the balance work.
 
If I was doing it again in (2000) I would have bought the lighter forged pistons (Ross or J&E at $600+) rather than the Speed-Pro (TRW $333) from Summit.
 
Now that we have the perfect AMC piston design from BullTear the $635 seems like a great deal and the best way to go IMHO.
Kirk P. Fletcher
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SC397 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/09/2012 at 8:18pm
I will never use Hyperutect pistons again.  They can't handle any detonation. 
I use the cast high compression '71 401 pistons in the '70 390's.  I will have to go through the numbers but I think it lowers the compression ratio down to like 9.5:1 which of coarse makes it less sensitive to detonation. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 440sixpack Quote  Post ReplyReply Direct Link To This Post Posted: Mar/09/2012 at 8:10pm
 I'm not sure the KB hyperutectics will be in the compression range you want  but if they are and you want to run them by all means  do they're great pistons . 
 
 Most guys problems with hyperutectics is they think they pour the nitrous to them or they don't file the top ring gap to specs. I've run them in my mopar big blocks for years turning 7500 rpm and HP that would tie an AMC V8 in knots  and NEVER a problem one.  I know many others with the same experience, hypers have gotten a bad rap for all the wrong reasons.
 
I'm going with Bulltear I think because I want about 10.0 and I'm using 58cc heads so the KB's don't quite get me there. if I was going to use my original 51cc heads then I'm a little too high so I'd have to cut the KB's and there again it's just easier to give Bulltear a call and get exactly what I want fron the start.
 
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